Lead-in conductor



Mam}! 1940- R. E. BASSETT. JR 7 2,193,017

LEAD-IN CONDUCTOR Original Filed Feb. 18, 1937 2 Sheets-Sheet ,1

iNVENTOR I Rex or/ 50888:: L/n BY m ATTORNEY March 12, 1940.

R. E. BAssETT. JR

LEAD-IN CONDUCTOR originai Filed Feb. 18, 1937 2 Sheets-Sheet 2 INVENTQRor/ Bassetzf L//- ATTORNEY Patented Mar. 12, 1940 UNITED STATES PATENTOFFICE Application February 18, 1937, Serial No. 126,352

Renewed August 8, 1939 3 Claims.

The present invention relates to radio aerials and particularly toimprovements in transmission lines and couplings used in theconstruction thereof. This application discloses an improvement upon theapparatus described in application Serial No. 99,571 filed in the nameof Rex Earl Bassett, Jr., on September 5, 1936, and is a continuation inpart of application Serial No. 99,571.

In order to improve both the transmission and reception of radiosignals, it has been found desirable to erect the antenna Where it is asfree as possible from local interference. Accordingly, transmissionlines have been utilized to transmit the signal energy to the antennafrom the transmitter and from the antenna to the receiver. Transmissionlines have been used extensively with antennae of the doublet type,which have been found very suitable for the reception of both short waveand the regular broadcast range frequencie Heretofore, a concentrictransmission line has usually consisted of a hollow tube of conductingmaterial with a conductor suspended axially thereof by suitableinsulators. Lines of this type not only are expensive to manufacture,but require a considerable outlay for upkeep. Usually they are filledwith dry nitrogen gas under pressure, to prevent dielectric failure dueto con densation of moisture inside the line.

Recently, transmission lines of the above type have been largelydisplaced by the twisted pair line, consisting merely of two insulatedwires twisted together. The insulation most often used has been rubber,but because of the susceptibility of rubber to atmospheric conditionsthe average life of the line is not very great. Collection of moisturebetween conductors causes it to function unsatisfactorily.

The principal object of the invention is to provide a new and improvedflexible transmission line that may be easily and efliciently secured toantennae.

Further objects and advantages of the invention are apparent from thedescription, in which reference is had to the accompanying drawingsillustrating preferred embodiments of the invention.

Fig. I of the drawings is a vertical section, showing a preferred formof the invention;

Fig. II is a fragmentary enlarged horizontal section taken on the line2-2 of Fig. I;

Fig.,III is a vertical section, showing a modifled form of theinvention; and

Fig. IV is an elevation, partly in section, showing the manner in whichthe terminal end of the device of Fig. III may be connected to theantenna.

These specific drawings and the specific description that follows are todisclose and illustrate the invention, and limitations upon the claims.

The preferred form of transmission line comprises a central conductorsurrounded by a layer of a flexible dielectric that is impervious towater, which is in turn surrounded by a flexible tubular conductor.

This construction enables the line to be connected to the antenna in asimple yet secure and highly effective fashion. The central conductormay be extended and partly uncovered to form a connecting portion forattachment to one of the terminals of the antenna, and the outerconductor may be suitably secured, as by soldering, to anotherconnecting portion for attachment to the other terminal. It is notnecessary to cover the junction of these connecting portions of thetransmission line with moisture proof material because of the layer ofimpervious dielectric between the conductors, but a body of rubber maybe molded thereabout to add strength to the connecting portions and toguard further against any interference with the operation of the linethrough deposition of moisture.

Even though moisture penetrates the outer conductor so that the outerconductor becomes thoroughly wet, the impervious dielectricsubstantially prevents the moisture from getting into the dielectricfield between the conductors, and there is no interference with theoperation of the line. No expensive waterproof outer coating isnecessary, and leaks in the outer coating are not to be feared. Inaddition, the layer of impervious dielectric is thick enough that itobviates interference from deposition of moisture in the crotch wherethe conductors lead outward to opposite branches of the antenna.

In Fig. I, a length of untinned No. 12 B and S gauge copper wire I isspirally or longitudinally wrapped with a layer of paper I! impregnatedwith varnish or Wax, to prevent the sulphation that is caused by sulphurpresent in the rubber. Surrounding the paper is a relatively thickcoating of rubber insulation it which is preferably good grade rubberhaving a low dielectric constant.

The rubber is covered by a flexible tube or sleeve 13 closely braidedfrom No. 30 tinned copper wire. This tube or sleeve constitutes theouter conductor of the concentric transmission line.

The tinning of the wire in the braided outer conductor l3 does notincrease appreciably the resistance of this portion of the transmissionline because of the relatively large diameter of the tube, but preventssulphation, like the layer of paper around the inner conductor, as wellknown to those skilled in the art. The central conductor i0 is untinned,because tinning makes are not to impose the radio frequency resistanceof that conductor too high.

The thickness of the rubber layer 12 may be varied as desired in orderto obtain a transmission line having a surge impedance matching that ofthe antenna. If rubber having a dielectric constant of 2.8, a centralconductor of No. 12 solid soft-drawn wire, and a braid of No. 30 wireare used the thickness of the dielectric must be .21 inch for animpedance of 62.5 ohms. The amount of power to be transmitted throughthe line of course determines the diameter of the inner conductor.

When the dielectric constant of the rubber is 2.8, the relationship ofthe surge impedance Z, the inside diameter D of the outer conductor, andthe outside diameter d of the inner conductor is as follows:

2:79 Log At the antenna end of the cable a central rubber coveredconductor, which may be formed by removing a length of the outerconductor l3, extends outward for several inches, and is bent at anangle of approximately 45 to the axis of the cable. Soldered to the endof the braided tube 13 is a piece of No. 12 copper wire 14, severalinches long, which diverges from the axis of the cable in the oppositedirection, likewise at an angle of about 45. Conductor M may be coveredwith a layer of waxed paper l I and a protecting sheath of rubber 12.

In the modified form of transmission line shown in Fig. III, the centralconductor i is surrounded by the layers of wax impregnated paper II andrubber compound 12. The rubber layer is surrounded by an anti-sulphationsheath of soft waxed cotton braid l5. Then the outer conductor l3 may bebraided over the cotton braid l5, and untinned copper wire may be usedtherefor.

To protect the copper braid, an outer covering 16 may be employed, whichneed not be waterproof, but may be composed of soft waxed cotton braid.

The terminal end of the line is made substantially weatherproof byextending conductor ID as in the previous modification, and providing adivergingconductor M, with a sheath l2 of rubber. A substantial lengthof the diverging portions of these conductors is surrounded by a body ofrubber compound I! that entirely prevents accumulation of watertherebetween. The described construction provides an integral rubberbody at the terminal end of the line that not only efiectively preventsthe aforesaid accumulation of moisture, but also acts to strengthen thecoupling. Exposed portions of the copper conductors to which the rubberis to be applied may be tinned.

The types of apparatus described immediately above are chiefly used withthe half Wave doublet antenna, which consists of two oppositelyextending conductors supported a predetermined distance above the groundand parallel thereto. A preferred mode of making the connection to theantenna is illustrated in Fig. IV, in which the transmission line ofFig. III is shown coupled to a doublet antenna comprising conductors I8and 19 secured to a cylindrical ceramic insulator 20. Insulator 20 isprovided with transverse holes 2| adjacent its ends to facilitate thesecuring of the conductors.

The transmission line is supported in the central cup-shaped depression22 adapted to receive the molded portion ll of the line, the cup-shapeddepression 22 being provided with a central aperture through which thetransmission line extends. The conductors l0 and M are secured to theantenna portions l8 and I9, as by soldering.

The concentric. transmission line described above is quite flexible andmay be handled rough- 1y without fear of injury thereto. It may beshipped like other flexible cable and out to desired lengths. It retainsits concentricity and its electrical constants remain unchanged evenafter repeated flexure.

The line is very easily attached to antennae already in position or toantennae installed with the line. It may be submerged in water or buriedin the earth, and its characteristics are not materially afiected by thepresence of moisture on its exterior, as the moisture cannot enter thedielectric field.

Changes in the illustrated embodiments may be made and other embodimentsof the substance of the invention may be devised to meet variousrequirements.

Having described my invention, I claim:

I. In an apparatus of the class described, a lead-in connectioncomprising a support, flexible central conducting means for connectionwith one portion of an aerial, a layer of rubber surrounding the centralconducting means, a tubular conductor enclosing the rubber layer, abranch conductor for connecting the tubular conductor with anotherportion of the aerial, and a body of rubber molded about the connectionbetween the tubular conductor and the branch conductor for sealing theconnection against moisture and retaining the central conductor on saidsupport.

2. In an apparatus of the class described, a lead-in connectioncomprising an insulation support having a substantially cone-shapedtransverse opening, flexible central conducting means for connectionwith one portion of an aerial extending upwardly and outwardly throughsaid opening, a layer of moisture-impervious solid dielectricsurrounding the central conducting means, a tubular conductorsurrounding the dielectric layer, a branch conductor for connecting thetubular conductor with another portion of the aerial, said connectionbeing substantially within the transverse opening and a body ofdielectric of substantial size molded about the connection between thetubular conductor and the branch conductor.

8. In an apparatus of the class described, a support having a transverseopening, a central copper conductor passing through said opening forconnection with one portion of an aerial, a layer of rubber of athickness predetermined in accordance with its dielectric constantsurrounding the central conductor, a braided tubular copper conductorenclosing the rubber layer, a branch conductor for connecting thetubular conductor with another portion of the aerial, a body of rubberof substantial size molded about the connection between the tubularconductor and the branch conductor and arranged to support said centralconductor in said transverse opening, and anti-sulphation layerssubstantially separatin the rubber from the copper surfaces.

REX EARL BASSETT, JR.

